1>What kind of foods should I feed my ranchus to improve and sustain their wen growth?
Presently, I am feeding hikari sinking pallets with floating pellets of another japanese brand. Most of my ranchus have good wen growth except the baby. One of my ranchu even has a hood that is so big that some of the wen is growing into the mouth and he really has a problem in feeding.

2>What kind of foods should I feed my ranchus to increase their body bulk?
I believe a certain percentage of this is attributed to genes. My Thai ranchu is round and imposing while the others(singapore bred) are more rectangular.

You are right that a lot of it has to do with genes. (and without sayng also perfect water quality ).

Besides the pelleted foods that you are using, feeding daily amounts of high protein foods, especially bloodworms, krill, plankton, beefheart, brine shrimp etc. etc. should help. variety can go a long way to help as well, so adding occasional veggies that you don't very often is a good choice as well.

you mean frozen beefheart mix like those for discus?

yes

however beefheart shouldn't be fed very often because of the possibility of "fatty liver", but besides that it is a great occasional food.